Silver recovery from spent, photographic processing fluids is known. Primary among the processing fluids high in silver concentration is the so-called "fixer" solution. This solution is used to dissolve out the unexposed and thus undeveloped silver halide of a photographic element in order to "fix" the image. Fixer solutions are usually acidic, e.g., due to the presence of acetic acid. Since silver is an important resource, and is expensive, numerous methods of recovering silver have been developed. These methods include two basic systems, one depending on electrolytic methods and the second utilizing a chemical replacement by a baser and less expensive metal; i.e., a metal higher in the electromotive series than silver. Both systems have advantages and disadvantages. The electrolytic system consumes electricity and that too can be expensive and is inefficient, with the effluent solution containing 200 ppm or more of silver. The chemical replacement system is also not generally efficient. Both systems, in addition, tend to produce a black, finely divided solid precipitate known as "black sludge" that plugs and clogs the system, and the solution containing more silver thus bypasses the system and is lost. This lost silver is not only economically disadvantageous but also represents a pollution problem and thus is ecologically unsound.
There is a need for an improved process for recovering silver from waste, acidic photographic processing fluids which is more efficient, economical and ecologically sound.